Process for rigid polyurethane foams

ABSTRACT

A process for the preparation of a fine celled, closed celled rigid polyurethane or urethane-modified polyisocyanate foam is disclosed which comprises reacting a polyfunctional isocyanate-reactive composition with a polyisocyanate composition, characterized in that the foam-forming composition comprises carbon black.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 08/554,535, filed Nov. 6, 1995 entitled "Process for RigidPolyurethane Foams", U.S. Pat. No. 5,604,265, which in turn is acontinuation of U.S. patent application Ser. No. 08/206,561 filed Mar.3, 1994.

DESCRIPTION

This invention relates to processes for the preparation of closed celledrigid polyurethane or urethane-modified polyisocyanurate foams, to foamsprepared thereby, and to novel compositions useful in said process.

Closed celled rigid polyurethane and urethane-modified polyisocyanuratefoams are in general prepared by reacting the appropriate polyisocyanateand polyol in the presence of a blowing agent. One use of such foams isas a thermal insulation medium as for example in the construction ofrefrigerated storage devices. The thermal insulating properties ofclosed celled rigid foams are dependent upon a number of factorsincluding the cell size and the thermal conductivity of the contents ofthe cells.

A class of materials which has been widely used as blowing agent in theproduction of rigid polyurethane and urethane-modified polyisocyanuratefoams is the fully halogenated chlorofluorocarbons, and in particulartrichlorofluoromethane (CFC-11). The exceptionally low thermalconductivity of these blowing agents, and in particular of CFC-11, hasenabled the preparation of rigid foams having very effective insulationproperties, Recent concern over the potential of chlorofluorocarbons tocause depletion of ozone in the atmosphere has led to an urgent need todevelop reaction systems in which chlorofluorocarbon blowing agents arereplaced by alternative blowing materials which are environmentallyacceptable and which also produce foams having the necessary propertiesfor the many applications in which they are used.

Such alternative blowing agents proposed in the prior art includehydrochlorofluorocarbons, hydrofluorocarbons and (cyclo)alkanes.Although these materials are environmentally more acceptable thanchlorofluorocarbons they are inferior in thermal insulation.

In order to improve the thermal insulation of closed celled rigidpolyurethane and urethane-modified polyisocyanurate foams blown withsuch alternative blowing agents a variety of techniques have beenproposed, most of them concentrated on decreasing the thermal radiationcomponent of the thermal conductivity of the rigid foam.

One of these techniques consists of adding carbon black to the foamformulation. The use of carbon black to improve the thermal insulationof closed celled rigid polyurethane foam is described in U.S. Pat. Nos4,795,763, 5,149,722 and 5,192,607 and Japanese patent publication KokaiNo. 57/147510.

The thermal conductivity reductions reported in these publications forclosed celled rigid polyurethane foams incorporating carbon black levelsbelow 5% by weight based on the total foam formulation are less than 8%.

Another way of decreasing the thermal radiation component consists ofdecreasing the foam cell sizes. Thus European patent publication No. 0508 649, U.S. Pat. Nos 4,981,879, 5,034,424 and 4,972,002 and Japanesepatent publications Kokai Nos. 91/743, 91/744, 91/745 and 91/746describe the use of a substantially fluorinated or perfluorinatedhydrocarbon additive as (co)-blowing agent or nucleating agent in closedcelled rigid polyurethane foam in order to reduce the foam cell size.However in view of the worse insulating properties of these additiveswhen used as (co)-blowing agent an improvement in thermal insulation ofthe foam is hardly obtained for closed celled rigid foam.

Therefore it is an object of the present invention to provide closedcelled rigid polyurethane or urethane-modified polyisocyanurate foamswhich have, even when blown with alternative environmentally acceptableblowing agents, the same or improved thermal insulation properties thanclosed celled rigid polyurethane or urethane-modified polyisocyanuratefoams blown with chlorofluorocarbons.

It is another object of the present invention to provide fine celledclosed celled polyurethane or urethane-modified polyisocyanurate foamshaving improved thermal insulation properties than the known fine celledclosed celled rigid polyurethane or urethane-modified polyisocyanuratefoams.

It is still another object of the present invention to provide carbonblack filled closed celled rigid polyurethane or urethane-modifiedpolyisocyanurate foams showing substantial thermal conductivityreductions.

The present invention provides a process for the preparation of a finecelled closed celled rigid polyurethane or urethane-modifiedpolyisocyanurate foam by reaction of a polyfunctionalisocyanate-reactive composition with a polyisocyanate compositioncharacterised in that the foam-forming composition comprises carbonblack.

By fine celled closed celled rigid polyurethane or urethane-modifiedpolyisocyanurate foam as used herein is meant closed celled rigidpolyurethane or urethane-modified polyisocyanurate foam having cells ofaverage diameter less than 150 micron, preferably less than 120 micronand more preferably less than 100 micron.

The cell size as used herein represents the isotropic diameter of thecell obtainable according to the method described by A. Cunningham in"Proceedings of Conference on Heat in Mass Transfer in Cryoengineeringand Refrigeration", September 1986, page 32-49.

By the process of the present invention fine celled closed celled carbonblack filled rigid polyurethane or urethane-modified polyisocyanuratefoams are obtained having substantially improved thermal insulationproperties compared to the known fine celled closed celled unfilledrigid polyurethane or urethane-modified polyisocyanurate foams of theprior art.

Some prior art descriptions of fine celled closed celled rigidpolyurethane or urethane-modified polyisocyanurate foams mention thepossible addition of fillers without however further exemplifying theparticular type of filler to be used (for example U.S. Pat. No4,981,879). Others (e.g. U.S. Pat. No. 4,972,002) give a list offillers, not including carbon black, to be used particularly asreinforcing filler and not to reduce the thermal conductivity of thefoam.

Further the relative improvement in thermal insulation obtained by theincorporation of carbon black in fine celled closed celled rigidpolyurethane or urethane-modified polyisocyanurate foams issubstantially higher than the relative improvement obtained by theincorporation of the same amount of carbon black (based on the totalfoam-forming composition) in closed celled rigid polyurethane orurethane-modified polyisocyanurate foams of normal cell size asdescribed in the prior art publications mentioned above. These prior artreferences do not mention the incorporation of carbon black in finecelled foam or suggest the substantial effect it may have in fine celledfoams compared to foams of normal cell size.

The carbon black may be any of the different kinds available, such aslampblack, channel black, gas furnace black, oil furnace black, thermalblack and graphitic carbon black. The particle size of the carbon blackparticles to be employed may vary, but generally the carbon black has amean particle diameter of from about 0.01 to 20 micron, preferably from0.02 to 3 micron and more preferably from 0.02 to 0.2 micron and evenmore preferably from 0.1 to 0.2 micron.

Preferred carbon blacks for use in the present process include furnaceblack SB250, furnace black SB550 and channel black SB4 (all availablefrom Degussa). Especially SB4 is preferred.

Typically the amount of the carbon black used in the process of thepresent invention ranges from 0.1 to 5%, preferably from 1 to 3% and ismost preferably about 2% by weight based on the total foam-formingcomposition.

A uniform carbon black dispersion in the finished foam product isessential for the significant improvement of insulation value inaccordance with the present invention. To produce the requisitehomogeneously filled foam, the carbon black is first uniformlydistributed in at least one of the foam-forming ingredients such as thepolyisocyanate composition or the isocyanate-reactive composition by anyconventional dispersing means. There may be added compounds which helpto disperse carbon black in the foam-forming ingredients such asdescribed in U.S. Pat. No. 5,149,722. Further the carbon black may besurface treated in order to improve the dispersing of the carbon blackin the foam-forming ingredients.

In order to obtain fine celled rigid foam an inert, insolublefluorinated compound is incorporated into the foam-forming mixture foruse in the present process.

The term inert as used herein with reference to the inert, insolublefluorinated compound used in the process of the invention is to beunderstood as indicating a substantial lack of chemical reactivity withany of the other components used in the foam-forming reaction.

The term insoluble as used herein with reference to the inert, insolublefluorinated compound used in the process of the present invention isdefined as showing a solubility in either the isocyanate-reactivecomposition or the polyisocyanate composition with which it is to beblended of less than 500 ppm by weight at 25° C. and atmosphericpressure.

Inert, insoluble fluorinated compounds for use in the process of theinvention include any of those disclosed in U.S. Pat. No. 4,981,879,U.S. Pat. No. 5,034,424, U.S. Pat. No. 4,972,002 and European PatentApplication No. 0508649.

It is preferred, however, to use an inert, insoluble, substantiallyfluorinated or perfluorinated compound having a boiling point of atleast 20° C. at atmospheric pressure, and preferably at least 40° C. andmore preferably at least 60° C., or 80° C. or 100° C.

The term substantially fluorinated as used herein with reference to theinert, insoluble, substantially fluorinated compound used in the processof the invention is to be understood to embrace compounds in which atleast 50% of the hydrogen atoms of the unfluorinated compounds arereplaced by fluorine.

Suitable compounds include substantially fluorinated or perfluorinatedhydrocarbons, substantially fluorinated or perfluorinated ethers,substantially fluorinated or perfluorinated tertiary amines,substantially fluorinated or perfluorinated amino-ethers andsubstantially fluorinated or perfluorinated sulphones.

Suitable examples of substantially fluorinated or perfluorinatedhydrocarbons are those containing from 1 to 15 carbon atoms, which maybe either cyclic or acyclic, either aromatic or aliphatic and eithersaturated or unsaturated, such as substantially fluorinated andperfluorinated methane, ethane, propane, butane, pentane, hexane,heptane, octane, nonane, decane, cyclobutane, cyclooctane, cyclohexane,cyclopentane, norbornadiene, decaline, dimethylcyclobutane,methylcyclohexane, 1-methyldecaline, phenanthrene, dimethylcyclobutane,and isomers thereof. Particular mention may be made ofperfluoro-n-pentane and perfluoro-n-hexane.

Suitable examples of substantially fluorinated or perfluorinated ethersare those containing from 3 to 15 carbon atoms, which may be cyclic oracyclic, such as substantially fluorinated or perfluorinated dialkylethers and alkyl substituted cyclic ethers. Particular mention may bemade of perfluorinated methyl ethyl ether, perfluorinated methyl propylether, the perfluorinated alkyltetrahydropyrans such as perfluorinatedpropyltetrahydropyran, and the perfluorinated alkyltetrahydrofurans suchas perfluorinated propyltetrahydrofuran and perfluorinatedbutyltetrahydrofuran. Additional examples of substantially fluorinatedor perfluorinated ethers which are suitable for use in the process ofthe invention are the commercially available fluorinated polyethers suchas Galden HT 100, HT 200, HT 230, HT 250 and HT 270 from Montefluos SpA(Galden is a Trade Mark).

Suitable examples of substantially fluorinated or perfluorinated aminesare tertiary amines containing from 3 to 15 carbon atoms, which may becyclic or acyclic, such as substantially fluorinated or perfluorinatedtrialkylamines, N-alkylated cyclic amines, tetraalkylhydrazines andtrialkylhydroxylamines. Particular mention may be made of substantiallyfluorinated or perfluorinated trimethylamine, triethylamine,ethyldimethylamine, methyldiethylamine, tripropylamine, tributylamine,tripentylamine, tetramethylhydrazine, trimethylhydroxylamine, O-ethyldimethylhydroxylamine, O,O'-bis-(dialkylamino)propylene-glycol,O,O'-bis-(dialkylamino)ethyleneglycol, N-methylpyrrolidine and theN-alkylpiperidines such as N-methylpiperidine.

Suitable examples of substantially fluorinated or perfluorinatedaminoethers include those having from 3 to 15 carbon atoms, which may becyclic or acyclic, such as substantially fluorinated or perfluorinatedtrialkylethanolamines and N-alkylmorpholines. Particular mention may bemade of substantially fluorinated or perfluorinatedtrimethylethanolamines and N-(C₁₋₆ alkyl)morpholines such as N-methyl,N-ethyl and N-isopropylmorpholine.

Suitable examples of substantially fluorinated or perfluorinatedsulphones include perfluorinated dialkylsulphones having from 2 to 8carbon atoms such as perfluoro-(dimethylsulphone) andperfluoro-(methyldiethyl-sulphone).

Certain inert, insoluble fluorinated compounds suitable for use in theprocess of the invention may themselves act as blowing agents under theconditions pertaining to the foam-forming reaction, particularly wheretheir boiling point is lower than the exotherm temperature achieved bythe reaction mixture. For the avoidance of doubt, such materials may,partly or completely, fulfil the function of blowing agent in additionto that of inert, insoluble fluorinated compound.

The amount of the inert, insoluble fluorinated compound used in theprocess of the present invention ranges from 0.05 to 10%, preferablyfrom 0.1 to 3%, most preferably from 0.1 to 2% by weight based on thetotal foam-forming composition.

Suitable organic polyisocyanates for use in the process include any ofthose known in the art for the preparation of rigid polyurethane orurethane-modified polyisocyanurate foams, and in particular the aromaticpolyisocyanates such as diphenylmethane diisocyanate in the form of its2,4'-, 2,2'- and 4,4'-isomers and mixtures thereof, the mixtures ofdiphenylmethane diisocyanates (MDI) and oligomers thereof known in theart as "crude" or polymeric MDI (polymethylene polyphenylenepolyisocyanates) having an isocyanate functionality of greater than 2,toluene diisocyanate in the form of its 2,4- and 2,6-isomers andmixtures thereof, 1,5-naphthalene diisocyanate and1,4-diisocyanatobenzene. Other organic polyisocyanates which may bementioned include the aliphatic diisocyanates such as isophoronediisocyanate, 1,6-diisocyanatohexane and4,4'-diisocyanatodicyclohexylmethane.

Polyfunctional isocyanate-reactive compositions for use in the processinclude any of those known in the art for the preparation of rigidpolyurethane or urethane-modified polyisocyanurate foams. Of particularimportance for the preparation of rigid foams are polyols and polyolmixtures having average hydroxyl numbers of from 300 to 1000, especiallyfrom 300 to 700 mg KOH/g, and hydroxyl functionalities of from 2 to 8,especially from 3 to 8. Suitable polyols have been fully described inthe prior art and include reaction products of alkylene oxides, forexample ethylene oxide and/or propylene oxide, with initiatorscontaining from 2 to 8 active hydrogen atoms per molecule. Suitableinitiators include: polyols, for example glycerol, trimethylolpropane,triethanolamine, pentaerythritol, sorbitol and sucrose; polyamines, forexample ethylene diamine, tolylene diamine, diaminodiphenylmethane andpolymethylene polyphenylene polyamines; and aminoalcohols, for exampleethanolamine and diethanolamine; and mixtures of such initiators. Othersuitable polymeric polyols include polyesters obtained by thecondensation of appropriate proportions of glycols and higherfunctionality polyols with dicarboxylic or polycarboxylic acids. Stillfurther suitable polymeric polyols include hydroxyl terminatedpolythioethers, polyamides, polyesteramides, polycarbonates,polyacetals, polyolefins and polysiloxanes. The quantities of thepolyisocyanate compositions and the polyfunctional isocyanate-reactivecompositions to be reacted will depend upon the nature of the rigidpolyurethane or urethane-modified polyisocyanurate foam to be producedand will be readily determined by those skilled in the art.

The process is carried out in the presence of any of the blowing agentsknown in the art for the preparation of rigid polyurethane orurethane-modified polyisocyanurate foams. Such blowing agents includewater or other carbon dioxide-evolving compounds, or inert low boilingcompounds having a boiling point of above -70° C. at atmosphericpressure.

Where water is used as blowing agent, the amount may be selected inknown manner to provide foams of the desired density, typical amountsbeing in the range from 0.05 to 5% by weight based on the total reactionsystem.

Suitable inert blowing agents include those well known and described inthe art, for example hydrocarbons, dialkyl ethers, alkyl alkanoates,aliphatic and cycloaliphatic hydrofluorocarbons,hydrochlorofluorocarbons, chlorofluorocarbons, hydrochlorocarbons andfluorine-containing ethers.

Suitable hydrocarbon blowing agents include lower aliphatic or cyclichydrocarbons such as pentane, iso-pentane, cyclopentane, neopentane,hexane, and cyclohexane.

Suitable dialkyl ethers to be used as blowing agents include compoundshaving from 2 to 6 carbon atoms. As examples of suitable ethers theremay be mentioned dimethyl ether, methyl ethyl ether, diethyl ether,methyl propyl ether, methyl isopropyl ether, ethyl propyl ether, ethylisopropyl ether, dipropyl ether, propyl isopropyl ether, diisopropylether, methyl butyl ether, methyl isobutyl ether, methyl t-butyl ether,ethyl butyl ether, ethyl isobutyl ether, and ethyl t-butyl ether.

Suitable alkyl alkanoates which may be used as blowing agents includemethyl formate, methyl acetate, ethyl formate and ethyl acetate.

Suitable hydrofluorocarbons which may be used as blowing agents includelower hydrofluoroalkanes, for example difluoromethane,1,2-difluoroethane, 1,1,1,4,4,4-hexafluorobutane, pentafluoroethane,1,1,1,2-tetrafluoroethane and 1,1,2,2-tetrafluoroethane.

Suitable hydrochlorofluorocarbons which may be used as blowing agentsinclude chlorodifluoromethane, 1,1-dichloro-2,2,2-trifluoroethane,1,1-dichloro-1-fluoroethane, 1-chloro-1,1-difluoroethane,1-chloro-2-fluoroethane, and 1,1,1,2-tetrafluoro-2-chloroethane.

Suitable chlorofluorocarbons which may be used as blowing agents includetrichlorofluoromethane, dichlorodifluoromethane,trichlorotrifluoroethane and tetrafluorodichloroethane.

Suitable hydrochlorocarbons which may be used as blowing agents include1- and 2-chloropropane.

Suitable fluorine-containing ethers which may be used as blowing agentsinclude bis-(trifluoromethyl) ether, trifluoromethyl difluoromethylether, methyl fluoromethyl ether, methyl trifluoromethyl ether,bis-(difluoromethyl) ether, fluoromethyl difluoromethyl ether, methyldifluoromethyl ether, bis-(fluoromethyl) ether, 2,2,2-trifluoroethyldifluoromethyl ether, pentafluoroethyl trifluoromethyl ether,pentafluoroethyl difluoromethyl ether, 1,1,2,2-tetrafluoroethyldifluoromethyl ether, 1,2,2,2-tetrafluoroethyl fluoromethyl ether,1,2,2-trifluoroethyl difluoromethyl ether, 1,1-difluoroethyl methylether, 1,1,1,3,3,3-hexafluoroprop-2-yl fluoromethyl ether.

Preferred blowing agents for use in the process are those having boilingpoints between -70° C. and +80° C. at atmospheric pressure.

In view of the improved thermal insulation properties associated withfoams prepared by the process of the invention, the use of fullyhalogenated chlorofluorocarbon blowing agents may advantageously beavoided.

Examples of preferred blowing agents include pentane, isopentane,cyclopentane, 1,1-dichloro-1-fluoroethane (HCFC 141b) and1,1,1,2-tetrafluoroethane (HFC 134a).

The total quantity of blowing agent to be used in a reaction system forproducing cellular polymeric materials will be readily determined bythose skilled in the art, but will typically be from 2 to 25% by weightbased on the total reaction system.

In addition to the polyisocyanate and polyfunctional isocyanate-reactivecompositions, the carbon black, the inert, insoluble fluorinatedcompound and the blowing agent, the foam-forming reaction mixture willcommonly contain one or more other auxiliaries or additives conventionalto formulations for the production of rigid polyurethane andurethane-modified polyisocyanurate foams. Such optional additivesinclude crosslinking agents, for examples low molecular weight polyolssuch as triethanolamine, foam-stabilising agents or surfactants, forexample siloxane-oxyalkylene copolymers, urethane catalysts, for exampletin compounds such as stannous octoate or dibutyltin dilaurate ortertiary amines such as dimethylcyclohexylamine or triethylene diamine,and fire retardants, for example halogenated alkyl phosphates such astris chloropropyl phosphate or alkyl phosphonates.

In order to stabilise the inert, insoluble fluorinated compound in oneof the foam-forming ingredients it is preferred to employ a surfactantin order to obtain an emulsion of this inert, insoluble fluorinatedcompound in the polyisocyanate or polyol composition.

Most preferred surfactants are fluorinated surfactants. Examples of suchsurfactants are fluorinated alkylpolyoxyethylene ethanols,alkylalkoxylates and alkylesters. Examples of useful fluorinatedsurfactants which are commercially available are Fluorad FC 430 and FC431 from 3M, Forafac 1110D, 1157, 1157N and 1199D from Atochem andFluowet S 3690, OTN and CD from Hoechst.

The amount of surfactant used is between 0.02 and 5 pbw per 100 pbw offoam forming reaction system and between 0.05 and 10 pbw per 100 pbw ofpolyisocyanate or polyol composition.

The foam-forming reaction mixture can also contain in addition to carbonblack or instead of carbon black other infrared absorbing materials inorder to reduce the thermal conductivity of the fine celled closedcelled rigid foam. Examples of such other infrared absorbing materialsinclude TiO₂, iron oxides such as Fe₂ O₃ and Fe₃ O₄, Cr_(x) Fe_(2-x)(x=0.3 to 2) mica, talc, copper, Al₂ O₃, Cr₂ O₃, Mn₂ O₃, MnO₂, ZrO₂,FeTiO₃, MgAl₂ O₄, CoAl₂ O₄, hydrated oxides such as FeO(OH), aluminumsilicate, metal carbides, metal silicides, metal nitrides, metal borides(especially Nickel and its alloys), metal cyanides such as Berlin Blue,metal fibres/flakes such as Al, Mn, Fe, Ni, Pd, Pt, Ag, Au fibres andorganic dyestuffs such as ultramarine and (metal) phthalocyanine, Nibis(dithiolene) complexes, polymethine dyes, heterocyclic cyanine dyes,croconium dyes and minerals of the kaolinite-halloysite series.

In operating the process for making rigid foams according to theinvention, the known one-shot, prepolymer or semi-prepolymer techniquesmay be used together with conventional mixing methods and the rigid foammay be produced in the form of slabstock, mouldings, cavity fillings,sprayed foam, frothed foam or laminates with other materials such ashardboard, plasterboard, plastics, paper or metal.

To reduce the number of component streams delivered to the final mixingapparatus, most of the additives such as the blowing agent, catalyst,fluorinated compound and carbon black and optionally others may bepremixed with one of the major components of the foam formulation, ingeneral with the isocyanate-reactive component.

Therefore the present invention also provides an isocyanate-reactivecomposition comprising an inert, insoluble fluorinated compound andfurther comprising carbon black dispersed therein.

The invention is illustrated but not limited by the following examples.

EXAMPLE 1 Preparation of Carbon Black Dispersions

21.6 g Solsperse 20K dispersant (available from Imperial ChemicalIndustries PLC) dried using rotary vacuum and 60 g toluene dried over amolecular sieve were added to a rotary vacuum flask and mixed at roomtemperature. 15 g SB4 carbon black (available from Degussa) driedovernight in an oven at 120° C. was then added and dispersed using lowshear mixing prior to placing in an ultrasonic bath for 30 minutes. Afurther 15 g of SB4 was then added to the flask and the ultrasonictreatment repeated for 1 hour. 62.5 g of polyol Daltolac XR144(available from Imperial Chemical Industries) was added to the obtaineddispersion and left to rotate on the rotavac at room temperature for 15minutes. The solvent was then removed under vacuum at oil bathtemperatures of 140° C.

The obtained carbon black dispersion (referred to hereinafter as CB 1)contained 55% by weight of polyol, 26% by weight of carbon black and 19%by weight of dispersant.

Another carbon black dispersion (referred to hereinafter as CB 2) wasprepared along the same lines, This dispersion contained 48% by weightof polyol, 14% by weight of carbon black, 12% by weight of dispersantand additionally 26% by weight of titaniumdioxide (RXL available fromTioxide).

Carbon black CB 3 referred to hereinafter represents Sigrafill carbonblack.

EXAMPLE 2 CFC 11 Blown Foams

Rigid polyurethane foams were prepared from the ingredients as indicatedin table 1 below (amounts are given in pbw).

As polyols were used Daltolac XR 159 and Daltolac XR144, both availablefrom Imperial Chemical Industries. As polyisocyanate was used SuprasecDNR available from Imperial Chemical Industries. As surfactants wereused B8404 available from Goldschmidt and FC 430, a fluorosurfactantavailable from 3M. As catalysts were used Niax Al, Catalyst SFB andCatalyst SFC, all available from Imperial Chemical Industries. Asfluorinated compound was used FC-87 (perfluoropentane) available from3M.

Results on foam density (in kg/m³), cell size (in micron) and thermalconductivity (initial lambda value in mW/m K) are also given in table 1.

                  TABLE 1                                                         ______________________________________                                        Foam  1      2      3    4    5    6    7    8    9                           ______________________________________                                        XR 159                                                                              50.0   50.0   50.0 50.0 50.0 50.0 50.0 50.0 50.0                        XR 144                                                                              50.0   50.0   32.1 39.5 19.4 30.8 38.9 17.8 50.0                        B8404 1.5    1.5    1.5  1.5  1.5  1.5  1.5  1.5  1.5                         Niax  0.1    0.1    0.1  0.1  0.1  0.1  0.1  0.1  0.1                         A1                                                                            SFB   2.4    2.4    2.4  2.4  2.4  2.4  2.4  2.4  2.4                         SFC   0.5    0.5    0.5  0.5  0.5  0.5  0.5  0.5  0.5                         FC 430                                                                              --     4.0    --   --   --   4.0  4.0  4.0  4.0                         Water 3.3    3.3    3.3  3.3  3.3  3.3  3.3  3.3  3.3                         FC 87 --     26.9   --   --   --   26.9 26.9 26.9 26.9                        CFC 11                                                                              25.3   12.6   25.3 25.3 25.3 12.6 12.6 12.6 12.6                        CB 1  --     --     32.6 --   --   35.1 --   --   --                          CB 2  --     --     --   22.0 64.3 --   23.4 68.4 --                          CB 3  --     --     --   --   --   --   --   --   9.2                         DNR   157    157    157  157  157  157  157  157  157                         Density                                                                             22.7   25.9   25.0 24.0 25.9 28.6 27.9 29.9 25.3                        Cell  406    161    426  459  474  144  148  143  155                         size                                                                          Lambda                                                                              18.0   19.2   18.2 18.7 21.9 16.0 18.1 17.9 18.6                        ______________________________________                                    

These results show that by using carbon black in fine celled closedcelled rigid polyurethane foam at loadings between 1 and 3% by weightbased on the total foam forming composition substantial reductions inthermal conductivity are obtained (foams nos 6, 7 and 8). In contrastherewith addition of the same amounts of carbon black to closed celledrigid polyurethane foam of normal cell size (foams nos 3, 4 and 5)doesn't reduce the thermal conductivity at all.

EXAMPLE 2 HCFC 141b and/or Water Blown Foams

Rigid polyurethane foams were prepared from the ingredients as indicatedin table 2 below (amounts are given in pbw).

As polyols were used Daltolac XR 159 and Daltolac XR144, both availablefrom Imperial Chemical Industries. As polyisocyanate was used aprepolymer derived from Suprasec DNR (available from Imperial ChemicalIndustries) and 2% by Weight of diethylene glycol (referred to herein asPrepolymer 1). As surfactants were used B8404 available from Goldschmidtand SCS 1294 available from Imperial Chemical Industries. As catalystswere used Niax Al, Catalyst SFB and Catalyst SFC, all available fromImperial Chemical Industries. As fluorinated compound was usedperfluorobutyltetrahydrofuran (referred to herein as PFBTHF) availablefrom Fluorochem Ltd.

Results on foam density (in kg/m³), cell size (in micron) and thermalconductivity (initial lambda value in mW/m K) are also given in table 2.

                  TABLE 2                                                         ______________________________________                                        Foam         10     11         12   13                                        ______________________________________                                        XR 159       50.0   50.0       50.0 50.0                                      XR 144       50.0   30.8       50.0 28.4                                      B8404        1.5    1.5        1.5  1.5                                       Niax A1      0.1    0.1        0.1  0.1                                       SFB          2.4    2.4        2.4  2.4                                       SFC          0.5    0.5        0.5  0.5                                       SCS 1294     2.0    2.0        2.0  2.0                                       Water        3.3    3.3        6.6  6.6                                       PFBTHF       7.6    7.6        7.6  7.6                                       HCFC 141b    21.5   21.5       --   --                                        CB 1         --     35.0       --   39.4                                      Prepolymer 1 168    168        224.5                                                                              224.5                                     Density      24.5   26.1       25.4 27.5                                      Cell size    139    127        230  220                                       Lambda       18.9   18.2       22.2 21.3                                      ______________________________________                                    

We claim:
 1. Polyfunctional isocyanate-reactive composition for thepreparation of fine celled closed celled rigid polyurethane orurethane-modified polyisocyanurate foam, wherein the cells of said foamhave an average diameter of less than 150 micron, comprising an inert,insoluble fluorinated compound characterized in that said compositionfurther comprises carbon black.
 2. An isocyanate-reactive composition asin claim 1, wherein said carbon black has a mean particle diameter offrom 0.02 to 3 micron.
 3. An isocyanate-reactive composition as in claim1, wherein the amount of carbon black ranges from 0.1 to 5% by weightbased on the total composition.
 4. An isocyanate-reactive composition asin claim 1, wherein said carbon black is surface treated.
 5. Anisocyanate-reactive composition as in claim 1, wherein said inert,insoluble fluorinated compound is selected from the group consisting ofsubstantially fluorinated or perfluorinated hydrocarbons, substantiallyfluorinated or perfluorinated ethers, substantially fluorinated orperfluorinated a/nines and substantially fluorinated or perfluorinatedamino-ethers.
 6. An isocyanate-reactive composition as in claim 5,wherein said inert, insoluble fluorinated compound is selected from thegroup consisting of perfluoro-n-pentane and perfluorinatedalkyltetrahydrofuran.
 7. An isocyanate-reactive composition as in claim1, wherein the amount of said inert, insoluble fluorinated compoundranges from 0.5 to 10% by weight based upon the total composition.